1. Technical Field
The present invention relates to a power transmission control apparatus, a power transmission apparatus, a contactless power transmission system, and a data determination method.
2. Related Art
Contactless power transmission that uses electromagnetic induction to transmit power without using a metal contact has come under the spotlight. As applications of contactless power transmission, charging of a cell phone, charging of a home appliance (e.g., a handset), and the like have been proposed.
A contactless power transmission apparatus using a primary coil and a secondary coil is described, for example, in JP-A-2006-60909. In the contactless power transmission system described in JP-A-2006-60909, a power transmission apparatus transmits data to a power reception apparatus by a frequency modulation. Also, the power reception apparatus transmits data to the power transmission apparatus by a load modulation.
The power reception apparatus described in JP-A-2006-60909 includes a variable load unit (load modulation unit) and turns on or off a MOS (metal oxide semiconductor) transistor for a load modulation provided in the variable load unit (load modulation unit) to transmit data to the power transmission apparatus via the secondary coil and primary coil.
When the load state of the power reception apparatus changes due to the turning-on or turning-off of the MOS transistor, for example, the voltage amplitude of the coil end of the primary coil is increased or reduced. On the other hand, the power transmission apparatus monitors the coil end voltage of the primary coil, for example, and compares the amplitude of the coil end voltage with a threshold, to determine whether data transmitted from the power reception apparatus is “0” or “1”.
The power transmission apparatus must reliably and rapidly determine data transmitted from the power reception apparatus using load modulation. Also, it is preferable that the configuration and operations of a data determination circuit provided in the power transmission apparatus be simplified as much as possible.
When the power transmission apparatus receives a communication packet transmitted from the power reception apparatus, for example, bit synchronization (initial synchronization) is first established and then data is determined on the basis of a signal (coil end signal) obtained from the coil end. For example, immediately after the power transmission apparatus starts, bit synchronization is yet to be established between the power transmission apparatus and power reception apparatus; therefore, first, a bit synchronization (initial synchronization) process must be performed to obtain a proper data determination timing.
Once a proper timing for determining received data is obtained by performing bit synchronization (initial synchronization), data transmitted from the power reception apparatus is preferably determined, for example, at predetermined intervals.
However, if an erroneous timing is obtained by performing bit synchronization (initial synchronization), data transmitted from the power reception apparatus can no longer be determined correctly. Therefore, it is necessary to obtain a proper data determination timing with caution and reliability in a process that has a large influence over later data determination timings, such as a bit synchronization (initial synchronization) process. On the other hand, a bit synchronization (initial synchronization) process must be performed efficiently and rapidly.
In addition to sending communication packets, the power reception apparatus may transmit periodic authentication data having a predetermined pattern to the power transmission apparatus periodically (e.g., every second). Periodic authentication is performed, for example, to detect a so-called “takeover state.”
Specifically, if, for example, a plate-shaped conductive foreign object (metal foreign object) having a large area is inserted between the primary coil and secondary coil after the power transmission apparatus starts normal power transmission to the power reception apparatus, the transmitted power is continuously consumed by the metal foreign object. Therefore, even after the power reception apparatus is removed, the power transmission apparatus determines that the power reception apparatus still exists as a load, and continues the normal power transmission. This state is called as a “takeover state.” The takeover state may heat the metal foreign object to a high temperature, causing a burn, a machine break, or the like.
For this reason, the power reception apparatus performs a periodic authentication process (a process of modulating the load periodically) and transmits data having a predetermined pattern (e.g., “0,” “1,” “0”) to the power transmission apparatus.
The power transmission apparatus detects whether a takeover state has occurred, depending on whether it can detect periodic authentication data periodically transmitted from the power reception apparatus. Specifically, once a takeover state occurs, periodic authentication data transmitted from the power reception apparatus no longer reaches the power transmission apparatus. Thus, the power transmission apparatus detects that the takeover state has occurred. Upon detection of the takeover state, the power transmission apparatus stops the normal power transmission.
When the power transmission apparatus first receives periodic authentication data transmission from the power reception apparatus, it must determine the periodic authentication data with caution and reliability to obtain a proper periodic authentication data determination timing, as in the above-mentioned bit synchronization (initial synchronization) process. Once a proper periodic authentication data determination timing is obtained, a periodic authentication data determination process is preferably performed, for example, at predetermined intervals.
However, the power transmission apparatus of the contactless power transmission system according to the related-art example cannot reliably and rapidly perform a bit synchronization (initial synchronization) process and, for example, a process of determining first received periodic authentication data.
Also, in the related-art example, the power transmission apparatus cannot receive a communication packet and periodic authentication data transmitted from the power reception apparatus, as distinguished from each other.